Folliculocentric squamous cell carcinoma with tricholemmal differentiation: a reappraisal of tricholemmal carcinoma

Abstract

Tricholemmal carcinoma is a rare occurrence, but it does exist, and at least one type of tricholemmal carcinoma is considered to be related to follicular (infundibular) SCC.

Follicular cutaneous squamous cell carcinoma: an under-recognized neoplasm arising from hair appendage structures

“…Tumours so defined were reported to arise mainly on the face and upper extremities of elderly patients. This type of carcinoma has only recently been described and, although mentioned in a few recent publications as well as Weedon's Skin Pathology , it continues to be a poorly recognized entity.…”

“…Histological criteria of FSCC (Fig. ) and its relation to infundibulocystic SCC were further investigated in studies by Misago et al ., who redefined the original criteria for both entities and concluded that FSCC and the less‐differentiated form of infundibulocystic SCC appear to represent the same neoplastic process . Others have emphasized a relationship of the epidermis to the infundibular follicular lining, raising a question as to the validity of new nosological entities of follicular or infundibulocystic SCC altogether .…”

Focus of tricholemmal differentiation (tricholemmal carcinoma) within Bowen's disease/carcinoma

“…We found the immunohistochemical profile in normal outer root sheath cells to be generally retained in these strictly selected tricholemmal carcinomas, except for CD34 . Similar to the normal hair follicles, tricholemmal carcinomas did not express CK1 expression, however, they did have a specific and uniform CK17 staining pattern (positivity in the inner or innermost clear cells of the neoplastic lobules) …”

“…We recently proposed that the diagnosis of tricholemmal carcinoma should be made according to the following strict diagnostic criteria: (i) pure folliculocentricity; (ii) primarily composed of clear/pale cells; (iii) columnar clear cells aligned in a palisade along a discernible basement membrane; (iv) tricholemmal keratinization; and (v) glycogen contained within the clear cells . We found the immunohistochemical profile in normal outer root sheath cells to be generally retained in these strictly selected tricholemmal carcinomas, except for CD34 .…”

Trichilemmal carcinoma: an unusual presentation of a rare cutaneous lesion

“…Consequently, several investigators have argued that the tumours described by Headington and later reported by others as TC were in fact clear-cell SCCs, which share several histological characteristics of ORS epithelium but are not truly ORS derived 11. To this end, some posited that TC cannot be distinguished from clear-cell SCC with absolute certainty until a specific marker for ORS differentiation is identified, while others have contested the existence of TC altogether 3 5. More recent histopathological studies, however, have confirmed the existence of TC as a distinct entity but have also concluded that its description in the literature may have been overstated, with true TC being even rarer than reports suggest, often being mistaken for other conditions that mimic TC 3 5…”